Since the pressure sensing part of the instrument is not in direct contact with the medium, and the heat will be controlled at room temperature during the pressure conduction process, the influence of the medium temperature of the flange transmitter on the instrument mainly depends on the nature of the liquid filled in the flange container. When the temperature of the measured medium exceeds the upper limit of the rated medium temperature of the instrument, two situations generally occur.
1) the filling liquid volume expands or even vaporizes due to heating. If the expansion is too large and the pressure exceeds the diaphragm's tolerance range, the isolation film can deform and in bad cases the filling fluid can be extruded from the joints and welds, resulting in complete damage to the equipment.
2) Filling liquid is an oily substance, containing more or less gas. In addition, it is impossible to vacuum the filling liquid before filling, and there will be a very small amount of gas dissolved in the medium. However, due to the extremely high thermal expansion coefficient of gas, even a trace amount of gas may cause the deformation of the isolation diaphragm.
To sum up, if the temperature of the measured medium exceeds the upper limit of the rated range of the instrument, even if the instrument is not immediately damaged, the diaphragm structure liquid may have been destroyed, leading to performance degradation. Once the equipment is found outside its rated temperature range, the equipment should be stopped using as soon as possible and the diaphragm should be checked. When choosing a flange pressure transmitter, it must be considered that the temperature of the liquid should not be lower than that of the medium under test. If the temperature of the medium under test is below the lower limit of the rated temperature of the instrument, the filling liquid will be frozen. In this way, when the pressure of the measured medium changes, the output changes of the instrument will be alleviated or even remain unchanged. But most instruments don't break. When the temperature of the measured medium returns to normal, the instrument will return to normal. If the instrument is to be used in extremely cold weather, consider the use of a hot band wrap diaphragm and a pressurized capillary to ensure that it operates in the normal temperature range.
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